HETL-2 - PAL 8-Field Timecode & Sc/H Phase Monitor

In videotape editing suites the correct phase relationship between Subcarrier, H-Phase and Timecode for Source and Record VTRs is essential for properly framed 8-Field edits without H-shifts, disturbances or edit aborts. This is particularly important when fieldstore/framestore timebase correctors are used since they can alter the phase of the video compared with the recorded timecode.

The HETL-2 display gives a permanent indication of the signal status on a colour-coded LED display which can be installed close to the operator. This avoids the annoying distraction of superimposing the display on the programme video monitor. Correct Phase is indicated by Green LEDs, Phase Errors by red and auxiliary functions by yellow.

The HETL-2 derives an 8-Field pulse (6¼Hz) from the external 8-Field EBU input which can be used to drive the editing controller.

Theory

The HETL-2 includes 2 decoders for the Timecode and Subcarrier Phase. Sync information is derived from the input video signal and fed to both decoders. One 6¼Hz pulse is generated from the timecode used to clock the timecode display decoder. A second 6¼Hz pulse is digitally derived from the input video subcarrier and used to clock the Sc/H Phase decoder. These reference pulses are then compared to give the relevant indications.

Specifications
Inputs:	Input Video Amplitude 700mV - 1.2V Return Loss >40dB @ 5.5MHz External 8-Field Ident Pulse >50µs, -ve going 1 - 4V p-p Timecode 500mV to 10V RMS Audio Input Impedance >50K ohm
Outputs:	Input Video Loopthrough 75 ohm BNC 8-Field Output Derived from 8-Field input Timecode Loop Through XLR balanced Remote Indicator Panel 25 pin D-type connector for all LED connections
Subcarrier / H Phase Monitor LED Indicators:	8-Field Ident Flag Present / 4-Field Error - Yellow Phase Indication 0° - Green ±45°, ±180° - Red
Timecode Monitor LED Indicators:	Colour Ident Flag (Bit 11) Present - Yellow Phase of Timecode (00:00:00:01) Field 1 (Standard A) - Green Field 2 - Red Field 3 (Non-Standard A) - Red Field 4 - Red Field 5 (Standard B) - Yellow Field 6 - Red Field 7 (Non-Standard B) - Red

All phase angles to within ±22.5° (EBU Specification for 8-Field editing).